1. Field of the Invention
The present invention relates generally to power transmissions and more specifically to continuously variable mechanical power transmissions.
2. Description of the Prior Art
A typical prior mechanical transmission is the sliding gear (standard) transmission. This standard transmission changes the input to output speed ratio in steps by manually changing gears. Power sources typically operate only over a small speed range with good economy and power. Therefore, a large number of gear changes are required for efficient operation. As an example, some trucks have numerous forward gears.
In addition to the standard transmission, certain stepless mechanical transmissions are also known.
One such device is disclosed in U.S. Pat. No. 4,565,105 of Peterson. In Peterson, a power transmission apparatus is disclosed for transmitting power from a reciprocable drive rod to a reciprocable output rod. This transmission includes a lever support, a fixed-length lever, and a fulcrum fixed to the lever for pivoting the lever to the lever support at a fixed location intermediate the end portions of the lever. One end portion of the lever is adapted for slidable connection to an end portion of the drive rod while another end portion of the lever is adapted for slidable connection to an end portion of the output rod. Also, a drive adjustment mechanism is included for shifting the lever support, and thereby the lever, relative to the input and output rods. This varies the throw of the output rods in response to reciprocations of the drive rod. To adjust this power transmission, the entire lever and fulcrum assembly is moved relative to the input and output loads. The fulcrum assembly is movable to a zero drive position in which the output rod remains stationary even as the input rod is driven.
Although offering a number of advantages, this prior Peterson transmission also suffers from a number of drawbacks. For example, the use of reciprocable input and output rods, as well as a fixed length lever, limits the ability to make the transmission compact. This is further compounded by the fact that the ends of the lever are shifted significantly beyond the locations which the lever is coupled to the drive and output rods during varying of the drive ratio of the transmission. Therefore, the transmission must be sized large enough to accommodate the ends of the levers during such shifting. Moreover, the drive rod extends outwardly from a cam which drives the rod and in a direction generally parallel to the plane of the cam. This also adds to the size of the transmission.
A still further device is disclosed in U.S. Pat. No. 1,401,538 of Kessler. In Kessler, a lever is pivoted at one end to a support and at its other end to a drive rod so that reciprocations of the drive rod cause the lever to oscillate. An output rod is provided and is slidably mounted to the lever intermediate its ends. As the lever support is raised and lowered, the lever slides relative to the output shaft. This movement of the support changes the output of the transmission by adjusting the throw of the output shaft.
Another prior art transmission device is shown in U.S. Pat. No. 491,759 of Prouty. In Prouty, a drive rod is pivoted to one end of a lever, which in turn is pivoted to a frame. An output rod has one end slidably connected to the lever. As this one end of the output rod is slid closer to and further from the lever pivot, the throw of the output rod is varied. In Prouty, the output rod is coupled to the lever for sliding to locations along the lever. The output rod is slidable from a position aligned with the pivot of the lever for zero output to other positions closer to the pivotal connection of the drive rod to the lever.
Still another existing device is shown in U.S. Pat. No. 2,254,195 of Cicin. Cicin includes a drive rod which reciprocates linearly and which is slidably connected to one end of the lever. An output rod has one end pivoted to the other end of the lever. The lever is slidably connected to a pivot and oscillates about this pivot. The pivot is movable from a position aligned with the output rod, in which case the output rod remains stationery as the input rod is driven, to various other positions along the lever. An adjustment mechanism is provided for shifting the pivot along the length of the lever. At the pivot, stresses on the lever are higher. Thus, to withstand certain loads, reinforcement of the lever along its entire length is indicated. This adds to the weight of the lever.
Therefore, although prior art variable transmission devices are known, a need exists for an improved, continuously variable, power transmission.